1. Field of the Invention
The present invention describes a continuous process for the preparation of a prepolymer based on oxazolines, epoxides and phenolic resins, using a catalyst, and also the use thereof.
2. Discussion of the Background
E. A. Boulter et al. in Electrical Insulation Conference, 1997, and Electrical Manufacturing & Coil Winding Conference Proceedings, Volumes 22-25 (September 1997), pages 249-253, describe the properties of oxazoline-modified phenolic resins, such as, for example, the adhesion to carbon fibres, glass fibres and metals, the resistance to thermooxidative degradation, the low level of smoke given off in the event of fire, the low flammability and the high impact strength. On account of the low flammability in particular these polymers are suitable for producing components for the aircraft industry. Further applications lie in the sector of electrical insulation and in the electronics sector. According to E. A. Boulter, these precursors and prepolymers are also suitable for applications including injection moulding, resin transfer moulding (RTM) and prepregs.
The reaction of difunctional oxazolines with phenolic resins is described in the literature. U.S. Pat. No. 4,699,970, for instance, describes the reaction of phenolic resins with 1,3-phenylenebisoxazoline in the presence of catalytic amounts of triphenyl phosphite. According to the examples, curing is carried out at a temperature of 225° C. The polymers obtained have a glass transition temperature of 138 to 184° C.
U.S. Pat. No. 5,302,687 likewise describes the reaction of 1,3-phenylenebisoxazoline with phenolic resin in the presence of phosphonium salts and/or ammonium salts. Here again, curing takes place, according to the examples, at 225° C., and again polymers are obtained that have a glass transition temperature of 150 to 157° C.
WO 2009/132924 describes a polymer composition comprising phenolic resin that comprises oxazolines and a stabilizer. Catalysts used are trialkyl or triaryl phosphites. This polymer composition is prepared preferably by means of an extruder.
WO 2009/053581 describes a resin composition composed of an epoxy resin and a plasticizer, the plasticizer having the function of dissolving the epoxy resin and influencing the viscosity. This resin composition may further be admixed with crosslinkers, such as 1,3-phenylenebisoxazolines, for example. Catalysts cited include Lewis bases and Lewis acids, such as boron trifluoride-monoethylamine, for example. The composition can be prepared by simple mixing. The curing temperature is not more than 195° C.
Hajime Kimura et al. in Journal of Applied Polymer Science, Vol. 107, 710-718 (2008) describe the preparation of a resin composition composed of bisoxazolines and benzoxazines, using a mixture of a sulphonic acid and an amino alcohol or alkylamine as catalyst (latent sulphonic acid). The resin is prepared by a batch process. The polymers obtained possess a glass transition temperature of between 149 and 186° C.